Combined deflecting device for cathode ray tubes



Jan. 10, 1939. R K 2,143,579

COMBINED DEFLECTING DEVICE FOR CATHODE RAY TUBES Filed Dec. 18,-1955 Patented Jan. 10, 1939 UNITED STATES.

COMBINED D G nnv rca ron EFLEOTIN CATHODE RAY TUBE Ernst Ruska, Berlin-Zehlendor'l', Germany Application December 18, 1935, Serial No. 55,009

In- Germany DecemberZO, 1934 2 Claims. (01. 250-27 This invention relates to combination-mag-- netic and electric beam deflecting systems for Braun tubes. The object of the invention is to provide a 5 system for deflection in two coordinates vertical to one another, and to combine maximum sensitivity with shortest length. Owing to the slight expenditure for sweep circuits resulting therefrom and the small length of the electron tube attainable thereby, considerable technical and economic advantages can be obtained, for instance when the tube'serves as scanning or reproducing member in television.

To attain its end the invention provides for 15 electric deflection of the cathode ray in one coordinate, preferably in the one having the higher frequency, and for magnetic deflection thereof in the other coordinate disposed vertically to the first. The main feature of the invention consists 20 in employing a magnetic and an electric deflect- The extent of these ing field coinciding in space. fields is limited to the space required for beam motion in deflection. For this purpose, ferromagnetic pole pieces having the same face as the 25 deflecting plates are arranged directly behind the plates of an electric deflecting system adapted to the beam deflection, or the plates themselves are constructed as magnetic pole pieces. The plates can either be insulated and seemed to the 30 front of the pole pieces, or the electric deflecting potentials are put on the pole pieces themselves, if the connecting magnet yoke or yokes are metallically interrupted at one point and the parts are electrically insulated relative to one another. 35 To keep down the magnetic resistance of the yoke, these interruptions must be as short as possible.

Furthermore, the sum of the insulation gaps should be as small as possible with respect to the 40 distance between the pole pieces, though, on the other hand, the capacity of .the parts on the electric control potential relative to their environment must not be too great.

These considerations determine the extent of l insulation. If the exciting coil is not to be brought into the vacuum, the pole piece deflecting plates are preferably continued almost up to the wall of the Braun tube, whereas the ferromagnetic yoke provided with the exciting wind- ;0 ings extends with both ends from outside closely up to the point of the inner pole pieces. In this construction, the wall of the tube serves therefore as yoke insulation, and the coil need not be put in the vacuum. The tube wall may have a 5 special form for this purpose.

If the coil is disposed in the vacuum, thewindings thereofmust be separated from one another and from the yoke by an insulation capable of withstanding the temperature developed during baking of the tube. Oxidation, e. g. copper oxide. 5 is suggested, it being possible for instance to wind the coil of bare wire and, following degasiflcation, to oxidize it by a controlled air pp y.

For extreme limitation of the space filled with the deflecting fields with respect to low inductance the face of the pole piece electrodes can be curved along the direction of the ray in such a way that a marginal electron of the pencil of rays falling into the system flows at the maxi: ll mum deflecting voltage between and along the two pole pieces. 4

By way of example, two embodiments of the invention are illustrated in the accompanying drawing,inwhichFlgurelisaviewoi'adeilecting system seen in the direction of the cathode; Fig. 2, a section on the line A-B, of Fig. 1; and Fig. 3, a view of another arrangement.

Referring to the drawing, in the embodiment according to Figs. 1 and 2 the deflecting system is located entirely inside the tube I. The ends of the pole pieces, designated 2 and 3, are constructed as deflecting plates and, with the interposition of the insulations l and 5, joined to the iron yoke 15 of the magnetic deflecting system. The inwardly disposed surfaces of the pole pieces serve also for the development of the electric field. The yoke is annular to fit the round neck of the tube and carries the exciting coils 6, I,

8, 9. Instead of the insulations l and 5, insulations may be provided at Ill and H or only at l2, and the coils 6, I and 8, 9 may each be replaced by a continuous coil.

A construction of a system with the coils arranged outside the vacuum is shown in Fig. 3. 40 The pole pieces l3 and M are extended up to the glass wall, and the yoke closely passes on the outside of the tube I of square cross section the end faces of the pole pieces, so that only a small air gap is formed by the glass wall.

Since it is one of the objects of the invention to build a Braun tube of smallest possible length, the combination deflecting fleld is made as wideangled as possible. Special attention is therefore paid to the marginal flelds which, to avoid spot distortion, must outwardly approach zero as quickly as possible. The magnetic figure of the marginal fields must, furthermore, be the same in all planes that are vertical to'the faces of the deflecting system. For this purpose, -ferromagas netic camber-electrodes areflndopmdiflznnd closely to, the pole piece (I: which both the electric and the magnetic max-31ml fleldcanterminate. Bunhconnbetm a mtermmedawn-wun' ofanelectric insulation "and II.

'lheoutlinelimitatiouotflieoounter-elechodes facing therayispretembiypamllqltothem ontheenteringsideoithesystannnd disclosesaboutthesamerelativedkhmeasthe polepieoeelectrodes. Onfheleavingsflgthe iii mnter-polescaflmaethevanishlinentthepolo ieces.

Acathoubmdeviceincmnlina- Iithncnflmdemtnbehnvlnganenvelope,

inwardb P jfi i from said faces up and mm and connecting means for mtoravaryinspotentialtosaklfamandmeanstoroontmllingthe aka-fields of said faces, comprising electrodes omnectedtosnidyokemidwaybetweensaidpoleshoes.

ERNST RUSKA. 

